Knapsack is one of essential personal belongings when people walk, hike and climb mountains, etc. Nowadays knapsack generally contacts directly with the knapsack's back, the knapsack is airtight, therefor it can not heat out, so that the knapsacker's back is sultry and sweat, it is very uncomfortable. To the end, people have developed cool knapsacks, for example CN00224778.X discloses a cooling massage knapsack comprising a bag body, a hollow slice, a plastic pipe, thread, buttons and rings, its characteristics is that when the knapsack is used, the air can circulate in the space among the hollow slice so as to play a cooling effect. For example, CN201520258085.3 discloses a cooling knapsack device, the knapsack is carried on knapsacker's shoulders with two straps, its structure consists of a pair of cross bars and a pair of straight rods, the pair of cross bars are respectively fixed on the upper part of the back of the knapsack and the lower part of the back of the knapsack, the pair of straight rods are respectively arranged at the left part of the pair of cross bars and the right part of the pair of cross bars, the straight rods are protruded outwards with a plurality of supporting blocks, the supporting blocks can be moved up and down and positioned along the straight rods and be fixed on them, what's more, the straight rods can also be moved left and right and positioned along the cross bar so as to adjust the position easily. The existing hard shell knapsack can be replaced by a frame support with a cross bar and a straight rod, which not only reduces weight but also has the benefit of protecting the goods in the knapsack from being damaged by pressure. In addition because of the spacing structure between the frame support and the knapsack it has the function of ventilation. Using the knapsack, the knapsacker will feel comfortable, cool and relief G-forces. It improves the using effect of the knapsack.
Although these knapsack solves the problems that the knapsack sticks the back of knapsacker at hot day, causing the knapsacker back hot, the cooling effect of these knapsack is not obvious. Especially when some articles that needed to be kept at low temperature are placed in the knapsack, it can not meet the requirement of freezing.